2 points in summoning give you access to dominate mind, soul mate and rallying cry.
3 very awesome skills =)
instead of 2 points plymoprh for wings you can also rely on cannibalize for nice survivability. use planar gateway to move around. those two points you save in poly and invest into summoning will greatly boost your summons and actually make them viable. descent damage and tankability all of a sudden.
Fire tree also has the fire slug available for you, which is a nice summon.
summoner actually has great support skills to help recover shield and health.
e.g: use soul mate on an ally in trouble then rallying cry on yourself and cannibalize for a nice burst heal of vitality magic and physical armor all at once.
charming is definitely the best cc there is, as you don't jus disable the victim, but also turn its cooldowns against the enemy team. so you prevent damage to your team redirect it to the enemy team and also spend the enemies cooldowns.
